In the prior art, there has been developed a device wherein a field of view is scanned to determine spectral and positional information of a point source of optical radiation. The field of view is optically scanned by a scanner having a narrow instantaneous field of view to sequentially direct radiation from different scanned portions of the field onto a single detector included in an image plane of the radiation. An optical dispersion means for the radiation is provided in a first optical path that includes the scanning means and the detector. A second optical path between source and detector includes a scanning means, but does not include the dispersion means. The dispersion means and the scanning means cause a convolution of spectral energy from the source on the image plane, resulting in a displacement of the relative occurrence times, during a scan, of a wavelength of the radiation as it impinges on the image plane via the two optical paths.
The optical scanner includes a multiplicity of focusing lenses that rotate together, about a fixed, centrally located detector. In the path of only one of the lenses, the dispersion means is provided to enable the spectral analysis to be performed. The remaining lenses enable the angular position of the source in the field of view to be determined. Determining the source position establishes a reference time during the portion of a scan while the dispersion means rotates in the field of view. The established reference time enables a correlation between spectral position and time to be made in the output of the detector while the dispersion means is in the field of view so that an amplitude versus time output of the detector can be correlated with amplitude versus wavelength response to the point source.
With the prior art system, it is difficult to establish a time position for the source while the dispersion prism is being rotated through the field of view of the detector. Also, the prior device does not provide for scanning in two orthogonal directions. A further problem with the prior art device is that it is incapable of distinguishing between point sources and nonpoint sources of optical radiation. As a result, nonpoint sources are susceptible of being processed as ponint sources, resulting in inaccurate amplitude versus spectral responses.